Double acting hydraulic cylinder with axial locking device

A double-acting hydraulic actuator comprising a cylinder body (2) closed at one end by an end wall (3) and at the other end by a cylinder head (4), a guide piston (7) slidably mounted in the cylinder body (2), an actuator rod (9) secured to the guide piston (7) and passing in leaktight manner through the cylinder head (4), hydraulic means for actuating the actuator rod (9), and mechanical locking means for locking the actuator rod (9) in a predetermined extended position, in which:

• a) the cylinder body (2) presents two coaxial cylindrical walls (26, 27) of different inside diameters and interconnected by a frustoconical annular section (25), the larger-diameter cylindrical wall (27) being placed beside the cylinder head (4) and the smaller-diameter cylindrical wall (26) serving to guide the guide piston (7);
• b) the actuator rod (9) presents an annular protuberance (33) between the guide piston (7) and the cylinder head (4), the diameter of the protuberance being not more than the diameter of the smaller-diameter cylindrical wall (26), said protuberance (33) being disposed in register with the larger-diameter cylindrical wall (27) when the actuator rod (9) is in the predetermined extended position;
• c) the guide piston (7) has means (30) putting both sides of said guide piston (7) into fluid communication;
• d) an annular piston is placed on portion (34) of the actuator rod that is situated between the guide piston (7) and the annular protuberance (33), the annular piston (40) being capable of sliding in leaktight manner against the smaller-diameter cylindrical wall (26) and being capable of sliding in leaktight manner against said portion (34) of the actuator rod under drive of pressure agent between a position in which the actuator rod (9) is released in which it bears against the guide piston (7), and a locked position in which it bears against the annular protuberance (33), said annular piston (40) presenting a narrowed end section (44) adjacent to the annular protuberance (33);
• and
• e) the locking means have locking members (41a, 41b) and means for urging said locking members (41a, 41b) to move radially, which locking members, in the released position of the actuator rod (9), are received axially between a radial face (36) of the protuberance (33) and the annular piston (40) and are housed radially between the portion (34) of the actuator rod and the smaller-diameter cylindrical wall (26), and in the locked position, are received radially between the larger-diameter cylindrical wall (27) and the narrowed end section (44) of the annular piston (40) and are housed axially between said radial face (36) of the protuberance (33) and the frustoconical section (25) of the cylinder body (2);
• the hydraulic actuator being characterized by the fact that the narrowed end section (44) of the annular piston (40) is cylindrical and is terminated by a conical surface (48) for co-operating with a conical surface (46) of the locking members (41a, 41b) so as to urge them radially outwards when the pressure agent acts on said annular piston (40) in the direction for extending the actuator rod (9).